1. Field of the Invention
The present invention relates to a method for transmitting a signal from a transmitting end in a multiple-input multiple-output (MIMO) mobile communication system which commonly uses a plurality of antennas at transmitting and receiving ends thereof.
2. Description of the Conventional Art
In this technical field, a multiple-input multiple-output (MIMO) mobile communication system has been known to be able to achieve remarkably improved properties compared with a single antenna system, namely, a single antenna versus single antenna or a single antenna versus plural antenna system. However, in order to achieve these improved properties, preferably, various signals which reach a plurality of receiving antennas are not correlated therebetween under substantial dispersion conditions, and when ignoring correlation between those signals even if the signals have some degree of correlation therebetween, performances of the system are degraded and capabilities thereof are decreased.
A related art multiple-input multiple-output mobile communication system (MIMO system) will be described in accordance with an embodiment as follows.
FIG. 1 illustrates a structure of a vertical bell laboratories space time (V-BLAST) system which is one of conventional arts of a multiple-input multiple-output (MIMO) mobile communication system.
The structure of a vertical bell laboratories space time (V-BLAST) system which is one of related arts of a MIMO system will be explained with reference to FIG. 1 as follows. The V-BLAST system belongs to the MIMO system, a technique including a plurality of transmitting/receiving antennas. Thus, the V-BLAST system uses M-numbered antennas at its transmitting end and N-numbered antennas at its receiving end. In this case, N≧M is assumed.
At the transmitting end, in order to transmit data, which is sequentially generated, with respect to data to be transmitted, a transmission data 11 pass through a vector encoder 10 (that is, the vector encoder 10 allows the data which is sequentially generated to pass through a serial-to-parallel circuit in order to transmit in parallel the data from each antenna), and accordingly different signals therebetween are transmitted from each antenna.
Here, modulation methods and the number of channelization codes of data transmitted to each antenna can be differently established, respectively. At this time, the channelization codes refer to codes having orthogonal properties as same as OVSF codes.
That is, when using a plurality of transmitting antennas 12, an additional signal processing or space-time code is not used, but each different signal with respect to data simply inputted is transmitted from different antennas. In other words, a transmitting end does not require the additional signal processing using correlation between antennas in order to improve a transmission quality.
That is, the transmitting end transmits different signals from respectively different antennas by using a plurality of antennas. The receiving end then receives the signals transmitted from the transmitted end through many antennas by using a separate algorithm, and appropriately detects the signals which have been differently transmitted through respectively different antennas at the transmitting end.
A V-BLAST receiving end signal processor 18 at the receiving end shown in FIG. 1 is for detecting signals which have been differently transmitted through M-numbered antennas, respectively, at the receiving end.
Now, on the other hand, an operation of the V-BLAST system will be described in more detail. A transmitting end of the V-BLAST system allows different signals to be transmitted from respectively different antennas with respect to data simply inputted, without using a diversity transmission technique such as an additional signal processing or a space-time code which uses correlation between antennas in each transmitting antenna.
At this time, modulation methods and the number of channelization method such as OVSF codes can be differently established for each antenna.
That is, if a downlink channel condition transmitted from a transmitting end antenna is known, data with a QAM modulation method and a high coding rate can be transmitted by using many OVSF codes with respect to antennas in a good channel condition, while in a bad channel condition, data with a QPSK modulation method and a low coding rate can be transmitted by using a few OVSF codes.
As a result, the transmitting end, as aforementioned, allows transmissions of respectively different signals from respectively different antennas by changing the modulation methods or the number of OVSF codes for each signal, and the receiving end detects signals having transmitted from each transmitting antenna through an appropriate signal processing.
Furthermore, explaining the appropriate signal processing at the receiving end, when detecting a signal transmitted from a specific transmitting antenna, a signal transmitted from another transmitting antenna is regarded as an interference signal. Afterwards, a weight vector of a receiving array antenna of the receiving end is calculated with respect to each signal transmitted from each antenna, and an influence of the previously-detected signal upon the receiving end is removed. As well as this method, a method for detecting signals transmitted from each transmitting antenna in the order of signals having a great signal-to-interference noise ratio can be used.
As above, when each transmitting antenna has different modulation method, coding rate, and the number of OVSF codes, information thereof has to be transmitted to a terminal over a downlink.
In the related art HSDPA (High Speed Downlink Packet Access) system, the information is transmitted through a HS-SCCH (HSDPA-Shared Control Channel). However, such HSDPA system does not assume a system structure having a plurality of transmitting/receiving antennas such as the MIMO system, information only for one antenna is transmitted through the HS-SCCH.
Unlike the HSDPA system, in the MIMO system, there can be established modulation methods, coding rates, the number of OVSF codes, or the like for the plurality of transmitting antennas, respectively. As a result, a control signal for each antenna is required.